The present invention relates to a method for detecting the end of etching, and more particularly the complete elimination, of a thin layer deposited on a substrate. The invention applies to the field of integrated circuit manufacturing, in particular to detect the end of the etching of a thin metallic layer deposited on a substrate having a rugged surface.
In a certain amount of operations involved in the manufacturing of integrated circuits, it is often necessary to etch a metallic layer deposited on a layer of insulating material. This is the case, for example, during the realization of a plurality of interconnection levels, in which one conventionally proceeds by etching parts of the metallic layer deposited on a silicon oxide layer which takes up the shape of the underlying structures and which consequently has a rugged surface. It is wished, in this case, to proceed with the etching operation until complete removal of this metallic layer is obtained in certain areas. It is nevertheless necessary to stop this etching operation rapidly after this complete removal of the metallic layer, because the continuation of this etching could modify or alter other structures and would uselessly prolong the duration of the manufacturing.
A difficulty is due to the fact that, in the final phase of the etching operation, the metallic layer subsists only in the form of very small size metallic residues. Usually, these residues are located near steps present in the underlying insulating layer. Because these residues are of small size, they are not detectable by conventional end of etching detection systems. Hence, to be certain that no residue remains after this etching operation, the etching of the metallic layer must classically be prolonged.
An object of the present invention is to provide a method for a precise determination of the complete elimination of a thin layer deposited on a substrate.
Another object of the present invention is to provide such a method which can be used as a controlling means for verifying if the etching operation has been satisfactorily carried out.
Another object of the present invention is to provide such a method which can be carried out in situ during the etching operation.